This project will test the hypothesis that reactive oxygen species (ROS) accumulation in aortic smooth muscle cells (SMCs) mediates the aortopathy in patients with bicuspid aortic valve (BAV). The interdisciplinary investigative team possesses a unique composition of expertise and has devised a novel approach to prove that ROS accumulation in BAV-ascending aortic aneurysm (TAA) specimens leads to de-differentiation of SMCs, abnormal extracellular matrix (ECM) composition and architecture and altered biomechanical strength of the aortic wall. The hypothesis is supported by the team's strong preliminary data demonstrating ROS accumulation, reduced cell viability in the presence of ROS, diminished oxidative stress responses, de- differentiation of SMCs, disrupted matrix architecture and altered biomechanical tensile and delamination strengths in the ascending aorta of BAV patients compared with tricuspid aortic valve (TAV)-TAA and non- aneurysmal patients. The innovative strategy is accomplished in a two-aim approach: 1) Define what changes in SMC phenotype, ECM composition and architecture, and biomechanical tensile and delamination strengths are associated with ROS accumulation in BAV aortopathy and 2) Prove that ROS accumulation in aortic SMCs mediates the BAV aortopathy. This study will exploit 1) the PI's extensive tissue bank of human ascending aortic specimens and primary SMCs isolated from the following patient cohorts: a) BAV-TAA compared with b) non-aneurysmal BAV, c) TAV-TAA, and d) non-aneurysmal TAV normal; and 2) the team's established scaffold-based 3-D tissue culture model. ROS will be evaluated using the investigators' expertise in electron paramagnetic resonance spin trapping and confocal microscopy of fluorescence-based ROS probes. Innovative assessment of ECM composition and architecture will be achieved using multi-photon microscopy with second harmonic generation to define alignment of collagen and elastin fibers, histological detection of collagen and elastin, and quantification of MMP activity. The team's pioneering techniques for studying blood vessel biomechanics will be utilized throughout the research design. This study will, for the first time, define and prove that ROS mechanisms mediate the BAV aortopathy. The results will potentiate significant long-term clinical benefits including the development of improved diagnostic tools for earlier detection and better surveillance of the BAV aortopathy and the discovery of pharmacologic therapies directed at modulation of ROS in the aortic wall to prevent aneurysm formation in BAV patients. PUBLIC HEALTH RELEVANCE: Bicuspid aortic valve (BAV) occurs in 1-2% of the population. The ascending aortas of BAV patients are uniformly larger in diameter compared to age- and sex-matched controls, and 45% percent of individuals requiring surgery to replace the ascending aorta because of thoracic aortic aneurysm or dissection have the congenital defect of BAV. Due to a lack of understanding of BAV-associated aortopathy at the cellular and molecular level, care of BAV patients has been limited to surgery only after the end-stage development of aneurysm or dissection thus resulting in a significant clinical problem worldwide: the hospital mortality rate after ascending aortic dissection is over 23% with and over 60% without surgical intervention representing the fifteenth leading cause of death in the United States. Discovery of the mechanism mediating BAV aortopathy will potentiate significant long-term clinical benefits including 1) the development of improved diagnostic tools for earlier detection and better surveillance and 2) the discovery of pharmacologic therapies to preserve aortic wall architecture and integrity to prevent aneurysm formation in BAV patients.